What is Rahu?

Rahu, I understand, is the NODE or point of intersection between Sun’s and Moons paths, where moon crosses the Ecliptic from South to North. So it is just a SPOT. There is nothing at the spot! I further understand that the position of Rahu in each consecutive Lunar orbit changes slightly, moving retrograde along the Ecliptic. This is the so-called motion of Rahu. Does the change in position move equally in each Orbit on Moon? I dont know.

I further understand that the location of Rahu goes around the Ecliptic , moving retrograde and takes about 18.6 years for one orbit of its own. I take it that these are Solar years. They equal how many Lunar months? 18.6 x 12 = 223 plus Adhik masas at 1 per 29 months or plus about 8 or total 231 lunar months or thereabout. If Rahu moves at a uniform rate, then each time it moves about 360/231 or 1.5 degrees approximately. After going round the Ecliptic does Rahu come back to the exact spot it started from? I dont think so but would like to know.

I am not sure of these calculations and would like to hear about them from readers.

My main question is different. Did our ancestors have the same concept about Rahu?

It is difficult to believe that thousands of years back, when there were no telescopes, anyone could identify a NODE of moon, leave aside its changing position per orbit of moon! So what did they understand by Rahu? Their concept was it was something which caused Solar Eclipse. We know that Solar Eclipse is caused by the moon coming between Sun and Earth. So was the old concept of Rahu, ‘something’ directly behind the moon as seen from earth? How do the ancestors describe motion of Rahu? How do they designate ‘location’ of Rahu at various times of the day month or year? I invite readers to throw some light on this issue.